1. Field of the Invention
The present invention relates to a sheet conveying apparatus used with an image forming apparatus such as an electrostatic copying machine, printer, facsimile and the like.
2. Related Background Art
In a conventional image forming apparatus as shown in FIG. 6, there is provided a both-face image forming function or a multi image forming function in which a sheet on which an image was formed in an image forming portion is conveyed again to the image forming portion, where an image is formed on the other surface of the sheet or on the same surface.
In a both-face copy mode or a multi copy mode, the sheet on which the toner images were formed and fixed are temporarily stacked on an intermediate tray. Thereafter, the sheets are separated one by one, and the separated sheet is introduced into a regist introduction path 116 through a both-face convey path 115. The regist introduction path 116 serves to send the sheet to a regist rollers in which, after being temporarily stopped, the sheet is sent to the image forming portion in synchronism with the operation of the image forming portion. Thereafter, the toner image is formed on the sheet again in the image forming portion. Then, the image is fixed to the sheet, and then, the sheet is discharged out of the image forming apparatus.
With this arrangement, if the sheet P is jammed or trapped between the both-face convey path 115 and the regist introduction path 116, a tip end of the sheet is detected by a sheet detection means 157 disposed in the vicinity of an outlet of the both-face convey path 115 or/and a sheet detection means 158 disposed in the vicinity of an inlet of the regist introduction path 116, thereby displaying (for an operator) a removal direction of the jammed sheet on an operation display portion (not shown).
For example, if the tip end of the sheet P is detected by the sheet detection means 157 associated with the both-face convey path 115 but is not detected by the sheet detection means 158 associated with the regist introduction path 116, on the basis of information displayed on the operation display portion, the both-face convey path 115 supported by a guide rail 118 for shifting movement in a horizontal direction perpendicular to a sheet conveying direction can be shifted or retracted, by the operator, toward a front side of the image forming apparatus along the guide rail 118. On the other hand, if the tip end is also detected by the sheet detection means 158 associated with the regist introduction path 116, on the basis of information displayed on the operation display portion, the operator can remove the jammed sheet from a right side of the image forming apparatus by opening a convey portion opening means (not shown) disposed at a right side of the regist introduction path 116.
However, in the above-mentioned conventional apparatuses, if the tip end of the sheet P is detected by the sheet detection means 157 associated with the both-face convey path 115 but is not detected by the sheet detection means 158 associated with the regist introduction path 116, when the both-face convey path 115 is retracted toward the front side of the apparatus, since a trail end of the sheet is pinched between convey rollers 154 and the like, the sheet itself will be retracted together with the both-face convey guide 115. As a result, if the tip end of the sheet is entered into a pre-introduction path 116A in front of the sheet detection means 158, the tip end of the sheet will be caught by a frame 102A for supporting the regist introduction path 116, thereby causing damage (folding or tearing) of the sheet. As a result, the jam treatment becomes more difficult.
As the case may be, a torn portion of the sheet P remains in the convey path. Under such a condition, if the copying operation is re-started, the sheet jam may occur again.
Further, in the above mentioned conventional apparatuses, it was devised that, by partially removing the frame 102A for supporting the regist introduction path 116, the tip end of the sheet P is prevented from being caught by the frame. In this case, however, the rigidity of the frame is decreased, thereby increasing vibration and noise of the apparatus and worsening the appearance of the apparatus.